Sunday, February 15, 2009

All was well in the world, because there were nine planets, and the ninth planet was Pluto

Neil deGrasse Tyson, the astronomer who "killed Pluto" (OMG!!) talks about how to define a planet, and why it really doesn't matter how many planets we have.

About why people were so upset about Pluto:
You know what I think it was? Because I put a fair amount of thought into this. When you learn something early in elementary school, and - you didn't learn what things were, you just memorized something - that's really what happened there. If you memorized something, and then later on that breaks, you feel like something attacked you. The memorization of the planets was kind of like an intellectual version of comfort food. All was well in the world, because there were nine planets, and the ninth planet was Pluto. And you memorized it. Had you learned that these were dynamic bodies, that had these properties, and then you learned that there were new objects that had new properties, I don't think people would have gotten upset. [..] My hope is that in the textbooks to come, there will not be an exercise in memorizing planets.
Which is a good excuse to link to Richard Feynman's essay on what science is.

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At 16 February, 2009 05:36 , Blogger Laurel Kornfeld said...

I agree that memorization is not a very useful method of learning, but I also strongly take issue with the statement that Tyson "killed Pluto" and with the controversial claim of some that Pluto is no longer a planet. As a writer and amateur astronomer, I have studied the properties of these objects, which is why I understand that the IAU demotion, done by four percent of its membership, most of whom are not planetary scientists, is so wrong.

First, it states that dwarf planets are not planets at all. That's like saying a grizzly bear is not a bear. It's also inconsistent with the use of the term "dwarf" in astronomy, as dwarf stars are still stars, and dwarf galaxies are still galaxies.

Second, the IAU definition classifies objects solely by where they are while ignoring what they are. If Earth were in Pluto's orbit, according to the IAU definition, it would not be a planet either. A definition that takes the same object and makes it a planet in one area and not a planet in another is terribly flawed.

The concept that an object has to "clear its orbit" to be a planet was concocted by dyamicists who want to artificially limit the number of planets in our solar system. It does not have scientific merit. That is why several hundred professional astronomers signed a petition immediately following the IAU decision rejecting it and saying they will not use it.

A far better planet definition is simply that a planet is a non-self-luminous spheroidal body orbiting a star. By that definition, we have 13 planets and counting in our solar system: Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, Haumea, Makemake, and Eris. It's fine to call the smaller, non-gravitationally dominant objects dwarf planets as long as we establish dwarf planets as one of many subcategories of planets (the others being terrestrial planets, gas giants, ice giants, etc.).

At 16 February, 2009 19:39 , Blogger Bjørn Stærk said...

Did you watch the video? The point is that it doesn't matter if it is a planet or not. That doesn't mean it's purely subjective, astronomers need to have a common, accurate terminology. And certainly one could choose other definitions. But for the general public (including amateur astronomers) to have strong opinions about this is ridiculous. Pluto remains Pluto. None of its properties have changed. If those properties interest you, what difference does it make how astronomers choose to group these objects?


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